Q1群落、結(jié)構(gòu)和穩(wěn)定性

Q1

群落、結(jié)構(gòu)和穩(wěn)定性要點(diǎn)群落群落（community）是在相同時(shí)間聚集在同一地段上的許多物種種群（speciespopulations）的集合。它的特性是由個(gè)體之間的相互作用如競(jìng)爭(zhēng)（competition）和寄生（parasitism）決定的。群落也能夠從更廣闊的角度和物種多樣性（speciesdiversity）、食物網(wǎng)（food-webs）、能量流（energyflow）和同資源種團(tuán)（guilds）中種間的相互作用來觀察它的特性。Thecommunityisanassemblageofspeciespopulationsthatoccurtogetherinthesameplaceatthesameplaceatthesametime.Ithaspropertiesdeterminedbytheimteractionsamongindividualssuchascompetitionandparasitism.Thecommunitycanalsobeviewedfromthebroaderperspectiveintermsofspeciesdiversity,food-webs,energyflowandtheinteractionsamongguildsofspecies.KeyNotesThecommunityQ1

THECPMMUNITY,STRUCTUREANDSTABILITY群落結(jié)構(gòu)一個(gè)群落的物種多樣性取決于群落含有的不同種的數(shù)量即種豐富度（thespeciesrichness）和種多度的均勻性（theevennessofspeciesabundance）。多樣性指數(shù)（diversityindices）可以通過這兩個(gè)因子計(jì)算出來。表達(dá)種豐富和種均勻度綜合的另一種方式是通過種的相對(duì)多度對(duì)種的順序作圖。多樣性能夠在局域群落（localcommunity）、地區(qū)（region）和最廣闊的地理尺度（geographicscale）（如大陸）三個(gè)不同的空間尺度上測(cè)算它。這樣就產(chǎn)生了a、β和Υ多樣性。Thespeciesdiversityofacommunitydependsonthenumberofdifferentspeciesitcontains(thespeciesrichness)andtheevennessofspeciesabundanceacrossspecies.Diversityindicescanbecalculatedtotakeintoaccountbothofthesefactors.Anotherwayofrepresentingspeciesrichnessandevennesstogetheristoplottherelativeabundanceofspeciesagainstrankorderofspeciesabundance.Diversitycanbemeasuredoverthethreedifferentspatialscalesofthelocalcommunity,theregionandthebroadestgeographicscale(e.g.thecontinent).Thisyieldsalpha(α)-,beta(β)-andgamma(γ)-diversity.Communitystructure群落邊界群落不會(huì)突然中斷，而是逐漸的過渡到其他群落，因?yàn)楦鱾€(gè)物種是逐漸受到它們的環(huán)境耐受力限制的。這一點(diǎn)可以通過梯度分析來得到證明，梯率分析重點(diǎn)在于物種分布重疊區(qū)域。分類和排序的統(tǒng)計(jì)方法允許群落的邊界在這個(gè)連續(xù)體上重疊。分類技術(shù)分出了生態(tài)學(xué)上不同的物種或地段，獲得了客觀等級(jí)。排序并不是企圖勾畫出邊界，而是根據(jù)它們?cè)诜植忌系南嗨菩远串嫵鑫锓N集團(tuán)或地段。Communitiesdonotendabruptlybutgradeintooneanotherasindividualspeciesencounterthelimitsoftheirenvironmentaltolerance.Thiscanbedemonstratedthroughgradientanalysis,whichfocusesontheoverlappingdistributionsofindividualspecies.Thestatisticalmethodsofclassificationandordinationallowcommunityboundariestobesuperimposedonthiscontinuum.Classificationtechniquesseparateecologicallydifferentspeciesorsitesyieldingobjectiveclasses.Ordinationdoesnotattempttodrawboundariesbutgroupsspeciesorsitesaccordingtohowsimilartheyareintheirdistributions.Communityboundaries同資源種團(tuán)同資源種團(tuán)是許多占據(jù)相似生態(tài)位的物種組合的集團(tuán)；如以闊葉樹為食物的許多昆蟲就形成一個(gè)同資源種團(tuán)。一些研究已經(jīng)表明，在一個(gè)群落內(nèi)的某些同資源種團(tuán)中的總物種的比例是不變的。這就表明也許有某一共同的“規(guī)則”在統(tǒng)治著群落結(jié)構(gòu)。Guildsaregroupsofspeciesthatoccupysimilarniches;forexample,insectsfeedingonbroad-leavedtreesformoneguild.Somestudieshavefoundconstancyintheproportionoftotalspeciesincertainguildswithinacommunity.Thisindicatesthattheremaybecertaincommon‘rules’governingcommunitystructure.Guilds群落的復(fù)雜性、多樣性和穩(wěn)定性穩(wěn)定性有兩個(gè)組成成分——恢復(fù)力（resilience）和抵抗力（resistance）。這兩個(gè)指標(biāo)描述了群落在受到干擾后的恢復(fù)能力和抵御變化的能力。復(fù)雜性被認(rèn)為是決定群落恢復(fù)力和抵抗力的重要因素。然而群落越復(fù)雜并不意味著群落越穩(wěn)定。復(fù)雜性增加已經(jīng)顯示會(huì)導(dǎo)致不穩(wěn)定。此外，群落的不同組分（如種豐富度和生物量）也許對(duì)干擾有不同反應(yīng)。具有較低生產(chǎn)力的群落（如凍原）其恢復(fù)力是最低的。相反，較弱的競(jìng)爭(zhēng)可以使許多的物種共存，從而減少群落的不穩(wěn)定性。茫茫的北極凍原Therearetowcomponentstostability–resilienceandresistance,whichdescribethecommunity’sabilitytorecoverfromdisturbanceandtoresistchange.Complexityisthoughttobeimportantindeterminingresilienceandresistance,However,morecomplexcommunitiesarenotnecessarilythemoststable;increasedcomplexityhasbeenshowntoleadtoinstability.Inaddition,differentcomponentsofthecommunities(e.g.speciesrichnessandbiomass)mayresponddifferentlytodisturbance.Communitieswithalowproductivity(e.g.tundra)tobetheleastresilient.Incontrast,weakcompetitionpermitscoexistenceamongspeciesandreducescommunityinstability.Communitycomplexity,diversityandstability相關(guān)主題資源分配（見I3）食物鏈（見P3）營(yíng)養(yǎng)復(fù)雜性與穩(wěn)定性食物鏈的長(zhǎng)度也許能夠影響群落的恢復(fù)力。具有不同營(yíng)養(yǎng)連接水平的許多群落模型，顯示復(fù)雜性導(dǎo)致恢復(fù)力和穩(wěn)定性下降。然而，這樣的研究應(yīng)該被謹(jǐn)慎地解釋，因?yàn)檎嬲娜郝渌哂械奶匦栽诹闳郝淠Ｐ椭胁]有被發(fā)現(xiàn)。穩(wěn)定性也依賴于環(huán)境狀況——一個(gè)脆弱的（復(fù)雜的或多樣的）群落也許能夠在一個(gè)穩(wěn)定和可預(yù)知的環(huán)境中持續(xù)下去，而在一個(gè)多變的和不可預(yù)知的環(huán)境中，僅僅簡(jiǎn)單的和生長(zhǎng)旺盛的群落才能夠生存下去。RelatedtopicsResourcepartitioning(I3)

Foodchains(P3)TrophiccomplexityandstabilityFoodchainlengthmayinfluencetheresilienceofthecommunity.Modelsofcommunitieswithdifferentlevelsoftrophicconnectanceshowthatcomplexityreducesresilienceandstability.However,suchstudiesshouldbeinterpretedwithcaution,asrealcommunitiesmsypossessimportantattributesmotfoundinthecommunitiesofnullmodels.Stabilityalsodependsonenvironmentalconditions–afragile(complexordiverse)communitymaypersistinastableandpredictableenvironment,whileinavariableandunpredictableenvironmentonlysimpleandrobustcommunitieswillsurvive.Q2

島嶼群落與移殖要點(diǎn)物種-面積關(guān)系島嶼上（或一個(gè)地區(qū)中）物種數(shù)目會(huì)隨著島嶼面積的增加而增加，最初增加十分迅速，當(dāng)物種接近該生境所能承受的最大數(shù)量時(shí)，增加將逐漸停止。物種數(shù)目的對(duì)數(shù)與面積對(duì)數(shù)的坐標(biāo)圖顯示的是一個(gè)線性關(guān)系。對(duì)于海洋島嶼和生境島嶼來說，這些雙對(duì)數(shù)坐標(biāo)圖直線的斜率，大多在0.24~0.34之間。對(duì)于連續(xù)生境內(nèi)的亞區(qū)域，斜率接近0.1。隨著面積增加，物種多樣性增加的效果在島嶼上要比連續(xù)生境內(nèi)明顯。島嶼Thenumberofspeciesonanisland(orinanyarea)willincreasewiththesizeoftheisland.Theincreaseisinitiallyrapid,tailingoffatthemaximumnumberofspeciesforagivenhabitat.Aplotoflogspeciesnumberagainstlogareagivesalinearrelationship.Foroceanicislandsorislandsofhabitat,theslopesoftheselog-logplotsmostlyfallwithintherange0.24-0.34.Forsubareaswithincontinuoushabitat,theslopeisaround0.1.Theeffectofincreasingspeciesdiversitywithincreasingareaismorepronouncedonislandsthanwithincontinuoushabitat.KeyNotesThespecies-arearelationshipQ2

ISLANDCOMMUNITIESANDCOLOMOZATION島嶼生物地理學(xué)麥克阿瑟和威爾遜的島嶼生物地理學(xué)理論指出，島嶼上物種的數(shù)目是由新移殖來的物種和以前存在物種的滅絕之間的動(dòng)態(tài)平衡決定的。當(dāng)移殖種的數(shù)目增加時(shí)，到達(dá)島嶼的移殖來的物種的數(shù)目會(huì)隨著時(shí)間的推移而減少。相反，當(dāng)物種之間的競(jìng)爭(zhēng)變得強(qiáng)烈時(shí)，滅絕的速率就會(huì)增加。當(dāng)滅絕和移殖的速率達(dá)到相等時(shí)，物種的數(shù)目就處于平衡穩(wěn)定狀態(tài)。模型研究也證明了物種的數(shù)目會(huì)隨著島嶼面積的增加而增加，和隨著距移殖者源距離的縮短而增加。對(duì)模型研究有利的證據(jù)，是由對(duì)除去動(dòng)物的島嶼上物種的再移殖的觀察，和對(duì)最近隔離的島嶼物種的喪失結(jié)果所提供的。當(dāng)與鄰近大陸對(duì)照的時(shí)候，滅絕和移殖過程說明了島嶼植物區(qū)系和動(dòng)物區(qū)系的衰亡。MacArthurandWilson’stheoryofislandbiogeographystatesthatthenumberofspeciesfoundonanislandisdeterminedbyadynamicequilibriumbetweentheimmigrationofnewcolonizingspeciesandtheextinctionofpreviouslyestablishedones.Asthenumberofcolonizingspeciesincreases,thenumberofimmigrantsarrivingontheislanddecreasesovertime.Incontrast,ascompetitionamongspeciesbecomesmoreintense,theextinctionrateincreases.Thepointatwhichextinctionandcolonizationratesareequalgivesthenumberofspeciesatequilibrium.themodelalsoaccountsfortheincreaseinspeciesnumberwithincreasingislandsizeanddecreasingdistancefromasourceofcolonists.Extinctionandcolonizationaccountforthedepauperatefloraandfaunaofislandswhencomparedtotheadjacentmainland.Islandbiogeography島嶼和異質(zhì)種群異質(zhì)種群理論已經(jīng)替代了島嶼生物地理學(xué)來解釋片斷化生境的“島嶼”種群行為。異質(zhì)種群含有許多種群，這些種群之間通過遷入和遷出而交換個(gè)體。與島嶼不同，生境斑塊（patch）是在景觀鑲嵌板塊（landscapemosaic）之中的，景觀板塊能夠影響斑塊的性質(zhì)和它所含的物種種類。相關(guān)主題種內(nèi)競(jìng)爭(zhēng)（見I2）保育對(duì)策（見V2）稀有物種、生境損失和滅絕（見V1）RelatedtopicsIntraspecificcompetition(I2)Conservationstrategies(V2)Rarespecies,habitatlossandextinction(V1)IslandsandmetapopulationsMetapopulationtheoryhassupersededislandbiogeographyinexplainingthebehaviorofpopulationsin‘islands’offragmentedhabitat.Ametapopulationconsistsofanumberofpopulationsthatexchangeindividualsthroughimmigrationandemigration.Unlikeislands,habitatpatchesareembeddedinalandscapemosaicthatcaninfluencethequalityofthepatchandthespeciesitwillcontain.Q3群落格局、競(jìng)爭(zhēng)和捕食要點(diǎn)群落集合集合規(guī)則（assemblyrule）的概念企圖解釋自然群落是如何不同于來自物種庫(kù)中的物種而隨機(jī)裝配出來的群落。群落集合也許能被生境類型、物種移殖和定居，或者種內(nèi)的相互關(guān)系，像捕食、寄生和競(jìng)爭(zhēng)所影響。集合規(guī)則研究群落組成中的格局，將那些由“零(null)”群落模型所產(chǎn)生的格局與真實(shí)的群落格局相比較。Theconceptofassemblyrulesattemptstoexplainhownaturalcommunitiesvaryfromrandomassemblagesderivedfromtherangeofavailablespecies(thespeciespool).Communityassemblymaybeinfluencedbyhabitattype,speciescolonizationandestablishment,and/orbyinterspecificrelationshipssuchaspredation,parasitismandcompetition,Assemblyrulestudiesinvestigatepatternsincommunitymake-up,comparingrealcommunitypatternswiththosegeneratedby‘null’communitymodels.KeyNotesCommunityassemblyQ3

COMMUNITYPATTERNS,COMPETITIONANDPREDATION競(jìng)爭(zhēng)競(jìng)爭(zhēng)可能是形成群落結(jié)構(gòu)的一個(gè)重要力量，但是在調(diào)查的時(shí)候，它又不一定是重要的。過去競(jìng)爭(zhēng)的痕跡在群落中可以留下很深的烙印（像生態(tài)位的分化）。競(jìng)爭(zhēng)的一些研究已經(jīng)表明，生態(tài)學(xué)上相似物種組成的同資源種團(tuán)當(dāng)中，僅僅只有一個(gè)成員在群落中能夠生存，這就意味著其他相似物種被競(jìng)爭(zhēng)排斥了。島嶼上超飄流的鳥類物種的分布也支持了該理論，即競(jìng)爭(zhēng)導(dǎo)致了群落的結(jié)構(gòu)化。新西蘭島嶼Competitioncanbeanimportantforceshapingcommunitystructurebutisnotnecessarilysignificantatthetimeofinvestigation.Theghostofcompetitionpastcanleaveastrongimprintonacommunity(e.g.asnichedifferentiation).Somestudiesofcompetitionhaveshownthatonlyonememberofaguildofecologicallysimilarspeciestendstobepresentinthecommunity,suggestiveofcompetitiveexclusionofothersimilarspecies.Thedistributionofsupertrampbirdspeciesonislandsalsosupportsthetheorythatcommunitiesarestructuredbycompetition.Competition食肉動(dòng)物選擇捕食和轉(zhuǎn)換獵物能夠使稀有物種免遭捕殺。這種行為能夠?qū)е略S多相對(duì)稀少的物種在同一個(gè)群落中共存。食草動(dòng)物食草動(dòng)物對(duì)植物群落有兩個(gè)作用：（i）它們選擇攝食影響群落的物種多度。（ii）啃食抑制了競(jìng)爭(zhēng)物種的生長(zhǎng)，因此加速和維持了低競(jìng)爭(zhēng)物種的多樣性。當(dāng)啃食強(qiáng)度很強(qiáng)時(shí)，物種多樣性降低，物種會(huì)局部滅絕。Grazinganimalshavetwoeffectsonplantcommunities:(i)theirselectivefeedingaffectsspeciesabundanceinthecommunity,and(ii)grazingsuppressesthegrowthofcompetitivespeciest